The present invention relates to a printed circuit substrate which is used in electrical circuits or optical circuits. Conventional circuitry of this type includes, for example, the substrate shown in FIG. 4. FIG. 4 is a cross-sectional view of one portion of a printed circuit substrate on which electrical circuits are formed.
Specifically, openings 2a, 2b are formed at prescribed positions in the printed circuit substrate 1', and a conductor 3, such as a copper foil, is printed onto the top and bottom surfaces of the printed circuit substrate 1' and interior surfaces of the holes 2a, 2b in accordance with the circuit wiring pattern as shown. This conductor 3 is formed by universally known printed wiring techniques such as, for example, etching and plating.
Furthermore, as shown in FIG. 4, a resistor 4 is connected to the printed circuit substrate 1' by lead wires 4a, 4b which are soldered into the aforementioned openings 2a, 2b. This resistor 4 forms a part of one of the electrical circuits.
However, in the abovementioned conventional circuitry, electrical circuits are formed by attaching circuit elements such as the aforementioned resistor 4 to the surface of the printed circuit substrate 1' after the aforementioned conductor 3 has been printed onto the substrate. As a result, unnecessary irregularities can be created on the surface of the printed circuit substrate 1' which interfere with the formation of a multilayer printed circuit board. Furthermore, there is a possibility that the printed circuit substrate 1' will be damaged by the heat generated by the soldering of the aforementioed lead wires. Moreover, in cases where soldering is insufficient, unsatisfactory electrical connections may result.
The present invention was conceived in light of the abovementioned problems encountered in conventional circuitry. The object of the present invention is to provide a printed circuit in which no unnecessary irregularities are created on the surface of the substrate, so that the formation of multilayer printed circuit boards is easily accomplished and in which unsatisfactory electrical connections are minimized.